Reflecting optical mirror system



July 24, 1951 F. 5, B 2,561,774

REFLECTING OPTICAL MIRROR Filed Nov. 23, 1949 FIG. I.

" i V M" INVENTOR ATTORNEYS Patented July 2 "1951 asrmc'mvo or'ncar.MIRROR SYSTEM Frank G. Back, New York, N. Y., asslgnor ,to F. G.

Back Video Corporation, New York, N. Y., a corr tation of New YorkApplication November 23, 1949, Serial No. 129,153

. a V 1 This invention relates to a new and improved optical system andoptical device.

object of this invention is to provide a mirror combination which can beused instead at a lens or lens system for many purposes. As

examples of some of said purposes, the improved mirror combination canbe used as a substitute tor a telephoto lens or a teleobiective inconnection with acamera oianytypesuchas a television camera, a camerawhich is used for taking still plcturea and a camera which is used o-taking motion pictures.

;The invention is or particular utility in conmetionwith a televisioncamera. A television has a standard television frame or 24 millimetersby 32 millimeters. A television camera ordinarily has a rotatable turretor turntable which carries four lenses. By turning said turret relativeto the television camera, a seiected lens of the turret is alined withthe photocathode or other part of the television camera or electronicpick-:up device which emits electrons,'or which is otherwise aflccted byor responsive to light.

m using a television camera. it is often necessary to change its fieldrapidly in order to secure rapid successive views of near and farobiects, and the turret must then be turned rapidly in order to selectthe proper lens which correto the distance from the television camera orthe object which is viewed.

I flitherto, it has beenimpossible to use a telephoto lens oi long focusin such a turret. The maximum iocai length oi such telephoto lens to!such purpose has been about 25 inches. This required a housing whoselength was 25 inches A telephoto lens 01 a focal length greater than 25inches is too heavy. and too long. --Byreason of such length and weight.such extra long telephoto'lens can not be flxedrlgidly to the turret, sothat such lens vibrates relative to the turret. such extra longtelephoto lens projects into the fields oi! the other lenses of theturret, andits resolution is interior, thus producing a picture oi.inferior clarity and quality.

The invention is preliminarily explained with to one embodiment, whichhas a concave mirror whose shape is a part of a sphere, and threeplanarmirrors. These planar mirrors are respectively designated as the first.second and third'planar mirrors. l'br' convenience, it is assumed thatthe longitudinalaxis of this concave mirror is horizontal. Since thedistance of the object from the vertex oi the spherical mirror exceedsthe radius Claims. ((11. ss-sv) oi curvature of the concave reflectingsurface 7 or said concave mirror, said concave mirror opcrates to form areal image of the object, which is intermediate the principal focus andthe center oi curvature of said concave mirror. This real image is bothvertically and laterally inverted. This real image is designated as theoriginal real image. 7

The first planar mirror may have any peripheral shape, such as circular,square. rectangular, etc. The axis of the concave mirror intersects thecenter of the first planar mirror, which prelerably extends equallyabove and below said axis. Said first planar mirror is located betweenthe vertex and the principal locus of said concave mirror. Said firstplanar mirror is inclined rearwardly and upwardly relative to the axisof the concave mirror. Said first planar mirror intercepts all the rayswhich are originally emitted by the object and which are initially.

reflected by the concave mirror, or a part of the rays which areoriginally emitted by the object and which are initially reflected bythe concave mirror. Said first planar mirror operates to form a firstreflected real image of the object, which is of the same size as theoriginal real image. The first planar mirror laterally inverts theoriginal real image. so that the first reflected real image is free fromlateral inversion The second planar mirror is located above the concavemirror, and said second planar mirror is axially or longitudinallyintermediate the first planar mirror and the concave mirror. This secondplanar mirror is rearwardly and downwardly inclined relative to thelongitudinalaxis oi the concave mirror, and said second planar mirrorreflects the light which is reflected thereto by the flrst planarmirror, downwardly in a direction which is perpendicular to said axis.The second planar mirror operates to form a second reflected real imageof the object. This second real image is laterally inverted.

The third planar mirror is located below the concave mirror and saidthird planar mirror is upwardly and rearwardly inclined relative to theaxis of the concave mirror. The second and third planar mirrors arevertically alined. The third planar mirror reflects the light which itreceives from the second planar mirror, rearwardly in a directionparallel to the longitudinal axis of the concave mirror. Said thirdplanar mirror operates to form a third reflected real image which isvertically inverted, but which is free from lateral inversion. Thisthird refiected real image is identical with the ori inal real image,save that the third reflected real image is laterally non-inverted.

The accurately focused third reflected real image is received upon atarget or receiving surface. If the improved device is used incombination with a television camera, the target or receiving surface isthe photocathode or other exit tube is offset relative to the concavemirror.

If the improved device is used in combination with -a television camera,the rear end of said exit tube, which is located rearwardly of theeasing, is clamped rigidly in one of the openings "of the turret. Thelight-receiving surface or member of the television camera can beadjusted relative to the third mirror, in a direction parallel to saidlongitudinal axis, in order to make allowance for diflerent distances ofdifl'erent respective objects from the vertex of the concave mirror.

' Ifthe light-sensitive surface is a photographic plate or fllm, suchlight-sensitive surface is similarly axially adjusted relative to thethird mirror. The concave mirror and the third planar mirrors anyperipheral shapes. The second planar mirror optionally and preferablyreflects all the light whichisreflectedbytheflrstplanarmirror, and

third planar mirror optionally and preferreflects all the light which isreflected by second planar mirror. The three planar mirare optionallyand preferably identical in all Instead of using a concave mirro whoseshape eated on the longitudinal axis of said paraboloid mirror, betweenthe vertex and the focus of said paraboloidmirror.

, The improved mirror combination provides sufficient tion so that itcan flll the standard television frame of 24 millimeters by 32millimeterawiththelmmeofamanwhoisata distance of 200 feet from thecamera.

Other objects and advantages and features of thh invention are disclosedin the annexed description and diagrammatic drawings, which illmtrate apreferred embodiment of the invention, when it is used as a substitutefor a telephoto lern of a television camera. In order to provide acomplete disclosure, the details of one practical embodiment are laterstated herein, including certain speciflc figures, but the invention isnot limited to such details and figures and many changes and omissionsand additions and substitutions' he made without departing from thescope of the invention.

Hg. 1 is a drawing of the improved optical 4 dinal optical axis of saidsystem is located. For convenience, said longitudinal optical axis X isshown in the horizontal position.

Fig. 2 is a side elevation which shows the improved optical unit fixedto the turret of a television camera.

The invention is explained in connection with an example in which theconcave reflecting surface of concave mirror 3 is a part of a spherewhose radius is inches, so that the focal length of said concavereflecting surface of mirror I is 40 inches. The horizontal optical axisX of the optical system is also the optical axis of mirror 8. Saidoptical axis X intersects the vertex is of the concave reflectingsurface of mirror I.

In this example. the mirror 3 has a circular edge 5, which is located ina vertical plane which is transverse to and perpendicular to thevertical plane of Fig. 1 and axis X. This transverse plane isperpendicular to axis x The object space 8 is in front of the frontelement i of the opt al system. This front element has a circular outerperiphery l, and it is colorless and transparent at an edge-portionwhose inner edge is deflned by a circular line to. The centers of therespective circular edges or periphries l and to are on axis X. g

This front element I. is optionally integral with a rearwardlyprojecting member I.

If front element I is not integral with said member M, said frontelement 0 may be a ring which is made of transparent and colorless glassor other material and whose outer and inner circular edges aredesignated by the lines 4 and la in'l 'ig. 1.

In this embodiment, the front and rear planar faces of member I, betweenthe concentric peripheral lines 4 and la, are deflned by the front andrear vertical lines It and lo, and said member i is of uniform thicknessabove and below the member M.

It is well-known that spherical aberration occurs when rays arereflected from a concave spherical or paraboloid mirror, especially whenthe mirror has a large aperture. It is optional to shape the member I,in order to correct or eliminate such spherical aberration of mirror I.Themirrorlmayalsobeshapedtocorrect or eliminate spherical aberration.

If the member M is made integral with member lsothatsaidmemberllismadeofgllls or of the other transparent andcolorless material of the edge-portion of member I between the lines 4and to, said member ll is provided-with a rear planar mirror surface lof metal or other opaque and light-reflecting material. Thisplanarmirrorfistheflrstplanarmirrorsurfacef.

Saidflrstplanarmirrorlisinclinedupwardly and rearwardly relative to axisx. and said planar mirrorfislocatedinatransvers'eplanewhichisperpendicular to the plane of Fig. 1.

Thebaseldof memberllisplanarandlocatcdinahorisontalplanewhichisperpendicularto the plane of Fig. 1. The partof member II which extendsrearwardlyoftherearverticallincfcisthereforeprism-shaped.

If the member I is made separately from the colorless and transparentmember I, said member i is ring-shaped. In such case, the memberMhasacircuiarflangebetweenthelinesfband 2c, which flts in the circularinternal periphery In of the colorless and transparent member I and suchflange of member if can be cemented mi m planeinwhichthel ns uorOtherwise ilxed to the wallofsaidcircular me m m. we e im EM mew we m. 1New M m mmmw mmmmmmmmm Wm WM m m M m m m m we m a m .A a we mm em mmmWWW m b. L M m m e m W m m m m umn mm m n w e E M m 7 m .3 W w e mmmmmmn w mfi mew M W 0 mm mmm wmwmmmmml m emmmmmkm m mmmm mmmmmme hmm WmWWW e mal 3 am m fie imam? m Mex mm mm mm 1 m m n mm m 0 mm mes m er m mu mm mm mm. m we mm m r e m emm .mm mmmm mme wmxmmmxm mu mm .mm l e cu ee eue ee- 4 memew s m. .mel m eflme eemem weamme .M m wmmwmmmm mflmmme mmw m m umi mmmfimm emmem mm m m mmm mm m L. m u m u w u m a m w w u d5., e e m m a e m 3 Tm e. mm Mm mm mmmmm M m e. e 1 ed nm mm mm om m e mw memmmmm m m m m m w m W m mm m mm m m wmm w m .1 e .m M xm L m e mm em M w w l mm mm xm mmmw mm mwmmmmmmm mmmmmmmmmm mm mm wm mm mm m Mm M 4ammmmwmmm ww mm m x b MW... nam mmmw n. Mmmmmmmmmn mmmmmmm .mmmw 1 a i mu if a d m m m m3 ummm mm am mam am, m mane mum mmmmmmwmmmmum mm extendsabout 2 inches to the rear of casipg D.

inches.

The .dlal netel' pfintemal peri her la is a The external diameter of theedge I of .er e mmmmm m m e". Je mehm mMe 7 1 muomna m ehM m w s me mmmmmmmm exam rm r 5 m mm m n mm m wmnm m mfi m m mm mm wlwu aa a mew Ememvmm e w mmm mmm w .m V. m h m The horlaontal distance between thevertical transverse planes of the vertical lines 2!; and 2c isOJSinch. I

The plane otfmlrror 2 is inclined by an angle 15915? to the verticalline 2c. This a beina'rangeot 1547. v a

horizontaldlstance of point Iairom line eexamine-n. 7

' The lensth of theside of mirror 2 which is M mm. 1 18 3.00 inches. Ifmirror! 18 a I tral Po 90 0f he ecu-me or In a television camera. saidcur-l face I maybe theelectron-emittinli' photocathode or otherlight-respon ive or light-sensitive surface or element of-apick-updevice. In a phicealnera. thevpoint leis thecen-.

tral point of theliaht-semitive surfaceof a pho tocrwhplstemrthecentrslpointoitheframe oftheiilmofamotionpicturecarnera.

In win: this emhodiinent,-it'is preferred tohavetheobiectwhichisbeingviewedorphotoraphed,:located in the frontobject space S,

at a distance of at least 70 feet in frontof the mmely the focal lengthof the mirror I. I

Iftheiinprovedopticaldevlceisusedincombination with a television camera,said improved optlcsldeviceisheldflxedrelativetothecaslns of the camera.The orthicon screen or other target or receiving surface of thetelevision camera orpick-upisadjustedinthecasingofthetelevision cameraTVC, in a direction parallel to the linelala.Ifthedeviceisusedwithaphotographic camera, the distance between pointsIa andoisadju'stedbytheusualmeansof thephotographic camera, by adjustingthe photographic.

plateoriilmrelativetothe point 1a,inadirectionparalleltoaxisxandaxism.Asabove A noted. the distances -36, tic-4a, la-la are notchanzed. v

WhentheohjectinthefrontspaceflissuflcientlyclosetovertexlmasmeasuredalongtheaxisxtheenteringraysAarenolongersubstantially parallel to axis x. Thedistances -811, 241-041, and la-Ia are maintained fixed.Thedistancelkiaisincreasedastheolpiect is'closer to vertex 8a. in orderto project the realimage of the object whichisformed by mirror'l..precisely upon the vertical planar frameoftheverticaltargetorverticaltransversereceiv'ing surface I of. thecamera; Thus, if the distanceofsaidobiectinspacesfrolnvertex In is '10feet, as measured along'axis I, the distance Ian-4a is increased so thatthesum of the distances inc-la, Io-ta, tc-Ia, Io-la is 42 inches.

-Fls.2sbowsthe turretTofthetelevisioncalnera 'I'VC. Said turret '1 isturnabie relative to thecasinxof the television camera TVC,aroImd'anaxtllwhichisparalleltotheopticalaxis I.Fig.2showsthehousingofanotherlensh whichisiixedtotheturretTWhentheimproveddeviceisinoperativepositionasshownatthetop'ofl'lmlitstubellocatedinandclampedinoneoftheopeninzs turretT.Thecasinz'nisthenollsetrelaits Dtowhichinirrorlbfltedorconnected.

oftubelislocatedintheopenincfinrretltheentirecasinaDextendsiorwardlyoftutret'lthroughadistancclessthanThkdistanceissoshortthatcasinc doesnotextendintotheneldsoftheother tube0, savefor the part of casing WM 01mm inwhicha"istheradhlofcurvatureotincident wave upon mirror 3, and"? is thediusofcurvatureofthereflectedwavewhichreiiectedbytheccncaveswfaceof-mirrori.

Itisamnncdthattheplaneoftheflrstplanar'mirrorlisinciinedfi'lfi'totbeverticallima,sothattheplaneofmirrorimakesanohtulc.angieofapproximatelylfi'wlthaxklandtlmttheobiectislccatedieetinfrontofvertexk asmeasuredalonaaxisXI-ntlntnidobiw b verticaLandthattheheightofsaidobjectisthrse'feet,andthatitscmtnlpointhonthelgidhidinalandhorisontalaxhx.Theconcavemirrorloperatesnnderthme conditionstoformailrstoriginalrealmmatelv 124 inches. namely, approximately 31withanangleoflessthanrtoazlsx. rays which are reflected by mirror 3angle of' approximately 4' withaxis X.

'Arayoflizhtwhichbemittedliythe pointofsaidobiectandwhichjustclearsedgeoftheiirstplanarmirror2,istherefore proximately coincidentwithaxisaxandwfll reflected by concave mirror '3 approximatelyoentralpointlcoitheflrstplanarmirrorl.

centraipointtcofmirrcrt' oftheorixinalrealimagewhlchwouldheformedbytheconcave-mirrorlintheahsenceofilrstplanarmirrortwouldbeapproximatelyfl incheatotheleftofpointloalongaidsx.

Hencetheoentralpolntoftheilrstrealreilcctedimazewhichwouldhefonnedbymplanarmirrorlifsecondpianarmirrorwuoomitted,wouidhealongthepathoftheraywhichisreilectedatpolntlmandatadktanceofapproximatelyflmchafrompotntla.Baideentralpointofsaidnrstreiiectedrealimagewouldbeapproximstelyliifiincheslaterallyaboveui lensesofthsturret'l.Themazimumic cth sxandapproaimatelyninchestotheriehtol olthcm a-deviceout departing from the central point on axis in avertical planewith itsA; andat the proper distance from the target or llrface l." I

By comparison with a lens, the angle of view of the improved'device withreference to the standerdteievsisionframemaybeverysmalhlessthan','as0.'l

l'br use in combination with a television camera, the maximum axialdistance from the casing D, as defined by line It, to the or to thecasing of the teievisioncamera is r the distance 2H1, it is possibledevice of even smaller size. I The above disclosure applies to the useof a panboloidmirrort.

.lihave referred to the use of three planar mirrors 2, land 1. This isthe hish ypreferred form. but the invention is'not limited to the useofthree planar mirrors. If one or more of said three mirrors isconcave-or convex, the variation from theplanar form is preferablyslight.

The specific example is particularly desirable when using a focussingconcave mirror whose focal length in 40 v I lave described a preferredembodiment of my invention, but numerous changes and omissions andadditions and" substitutions can be made withscope of my invention.

1. An optical device which comprises a concave which has a concavereflecting surface which has a geometrical vertex and an axis and aprincipal focus which is located on said axis in front'of said vertex, afirst mirror located forwardly of said concave mirror and rearwardly ofsaid principal focus, said first mirror being thus lomted to-interceptlight which isforwardiy re- I0 L whichisfree fromlateralinversionalongsaidpath.

2, Anoptical device according to claim 1. in

respectivelateraldistancesofthcseca. a optical to claim 1, in'

oi'saidprincipalfocuasaidfirstmirrorbeing thus located to interceptlight which is forwardly reflected from said concave mirror, said firstmirrorbeinginclinedtosaidaxisandbeingofsuiiiciently smallsize to leave apart of saidconcave mirror unblocked to receive incident rays from anobject located forwardly of said first minor, a second mirror locatedforwardly of said concave mirror and rearwardly of said principal focus.a third mirror located forwardly of said concave mirror and rearwardlyof said principal focus, said second mirror and said third mirror beinglocated laterally on opposite sides of said axis. said secondmirror'beinglocated and inclined to said axis to intercept thelightwhich is reflected from said first mirror and to reflect sald'lighttosaidthirdmirror,saidthirdmirrorbelnglocated to reflect the light whichit receives from said-secondmirrorinapathwhichclearssaid concave mirror,said first and second and third mirrors being shaped and located toproduce a projected real image by said third mirror which is free fromlateral inversion along said pathQsaid .path being substantiallyparallel'to said axis. and

' said third mirror being located to produce said ficcted i'romsaidconcave mirror, said first mirror a to said axis and being ofsufficiently small siae to leave apart of said'concave mirror unblockedto receive-incident'rays from an object j heated forwardly of said firstmirror. a second Jnii'r'or' located'forwardly of said concave mirror andrearwardly of said principal-focus, a third mirroriocated forwardly ofsaid concave mirror.

and rearwardly of said principal focus, said secand mirror and'saidthird mirror beinglocated literally on opposite sides of said axis, saidseccndmirrorbeinglocatedandinclinedtcsaidaxis to intercept thought whichis reflected from said second mirror and to reflect said light to saidthird mirror, said third mirror being located to reflect the light whichitreceives from said second mirror in a path which clears said concavemirror,

Iidfirstandsecondandthirdmirrorsbeing shaped and located to produce aprojection real prgmtcd real image rearwardly of said concave -m 5.'Anoptical device which comprises a concave mirror .which has a concavereflecting surface which has'a geometrical vertex-and an axis and aprincipal focus whichis located on said axis in front of said vertex,thefo'cal length of said concave mirror being substantially 40 inches, afirst planar-mirror located forwardly of said concave mirror andrearwardly of said principal focus to intercept light which is forwardlyreflected from said concave mirror, said axis intersecting substantiallythe central point of said first mirror, said first mirror being inclinedto saidlaxis at an angle of substantially 15 to 17, the edgev of thereflecting surface of said concave mirror having a diameter ofsubstantially Binches, the top and bottom points of said first mirrorbeing substantially 1.46 inches laterally from said axis. the axialdistance between the center of said first mirror and the vertex of saidconcave mirror being substantially 13 inches to 14 inches, secondmenu ofsaid stop-plate and being turnably adjustable to block an annular areaof said concave mirror around the blocked part thereof, said firstmirror being inclined to said optical axis and bein of suflicient smallsize to leave a part of said concave mirror unblocked to receiveincident rays from an object located forwardly of said first mirror, asecond and third mirror located laterally on opposite sides of saidoptical axis and also located forwardly of said concave mirror andrearwardly of said first mirror, said second mirror being located andinclined to said optical axis to intercept light which is reflected fromsaid first mirror and to reflect said light to said third mirror, saidthird mirror being located to reflect the light which it receives fromsaid second mirror in a path which clears said concave mirror, the pathsor light reflected from said first and second and third mirrors clearingsaid stop 14 plate, said first and second and third mirrors being shapedand located to produce a projected real image which is free from lateralinversion.

FRANK G. BACK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 625,627 Woody May 23, 18991,551,291 Evans Aug. 25, 1925 1,591,211 Brenkert et al July 6, 19262,152,202 Miller Mar. 28, 1939 2,309,788 Ramberg Feb. 2, 1943 2,409,186Bouwers Oct. 15, 1946 2,504,384 Bouwers Apr. 18, 1950

